In recent years the use of liquid crystal display devices has spread rapidly not only in information and telecommunications equipment but in ordinary electric equipment as well. Because liquid crystal display devices do not themselves emit light, use is often made of transmissive liquid crystal display devices that are equipped with a backlight. The power consumption of backlights is large, however. Accordingly, reflective liquid crystal display devices, which do not require a backlight, are employed in order to reduce power consumption, especially with portable equipment. But in dim room interiors these reflective liquid crystal display devices are hard to view, because they use external light as their light source. Over recent years therefore, especial progress has been made with development of semitransmissive liquid crystal display devices, which combine the properties of the transmissive type and the reflective type.
The liquid crystal display panel used in these semitransmissive liquid crystal display devices has, within each pixel area, a transmissive section equipped with a pixel electrode, and a reflective section equipped with both a pixel electrode and a reflecting plate. In dark places it lights a backlight and uses the transmissive sections of its pixel areas to display images, while in bright places it uses external light from the reflective sections to display images, without lighting the backlight. Thus there is no need for the backlight to be constantly lit, and consequently this panel has the merit of greatly reducing power consumption.
However, in the small-size display sections of mobile equipment, typified by mobile telephones and the like, there was previously no very large demand for the liquid crystal display panel to have a wide viewing angle, because such equipment had a limited number of users, and for related reasons. But with the increasingly functionally sophisticated mobile equipment of recent years, the demand for a wide viewing angle for the display section's liquid crystal display panel has grown rapidly. In response to such demand for a wider viewing angle for mobile equipment, efforts have been ongoing recently to develop MVA semitransmissive liquid crystal display panels to replace the TN liquid crystal display panels hitherto widely used in mobile equipment (see JP-2003-167253-A (claims, paragraphs [0050] to [0057], FIG. 1) and JP-2004-069767-A (claims, paragraphs [0044] to [0053], FIG. 1)).
The MVA semitransmissive liquid crystal display panel disclosed in JP-2004-069767-A will now be described using FIGS. 4 and 5. FIG. 4A is a perspective view illustrating the approximate structure of an MVA semitransmissive liquid crystal display panel 50, FIG. 4B is a schematic view illustrating the inclined state of the liquid crystals when an electrical field is applied to the liquid crystals of the liquid crystal layer, and FIG. 5 is a cross-sectional view along V-V in FIG. 4A.
In this semitransmissive liquid crystal display panel 50, an inclined surface or step difference 53 is provided between a reflective section 51 and a transmissive section 52, and the reflective section 51 and transmissive section 52 are connected via the step difference 53. In the pixel electrode 55 of a first substrate 54 in the semitransmissive liquid crystal display panel 50 there is formed a first open region 56, being an area where the pixel electrode 55 is not formed. This first open region 56 constitutes a first orienting/dividing structure, and is formed so as to lie on either side of the step difference 53 and to straddle the reflective section 51 and transmissive section 52. As a result, the pixel electrode 55a in the reflective section 51 and the pixel electrode 55b in the transmissive section 52 are connected to each other via a single line 57 extending in the longitudinal direction of the semitransmissive liquid crystal display panel 50.
In the opposing electrode 59 of a second substrate 58 there are formed second open regions 60a and 60b, in locations opposite the pixel electrode 55a in the reflective section 51 and the pixel electrode 55b in the transmissive section 52, respectively. These second open regions 60a, 60b constitute a second orienting/dividing structure. The second open regions 60a, 60b are formed as cross-shaped slits, and are so arranged that the center of second open area 60a is aligned with the center of pixel electrode 55a and the center of second open area 60b is aligned with the center of pixel electrode 55b. 
When an electrical field is applied to the liquid crystals 61 of the liquid crystal layer in this semitransmissive liquid crystal display panel 50, since the dielectric anisotropy of the liquid crystals 61 is negative, over the first open region 56 at the step difference 53 the liquid crystals incline toward the line 57 on the opposing electrode 59 side, while over the reflective section 51 and transmissive section 52, the liquid crystals incline to the center of the opposing electrode 59's region corresponding to the reflective section 51 or to the center of the region corresponding to the transmissive section 52, as shown in FIGS. 4B and 5. Thus, in the semitransmissive liquid crystal display panel 50, the orientation directions of the liquid crystal molecules are determined, and therefore it is possible to reduce degradation of visual characteristics and deterioration of response speed.
The foregoing MVA semitransmissive liquid crystal display panel 50 is provided with a step difference 53 between the reflective section 51 and the transmissive section 52 on the first substrate 54, and, as is commonly known, is so configured that the cell gap d1 in the reflective section 51 and cell gap d2 in the transmissive section are in the relation d1=(d2)/2, thus being adjusted so that the display quality in the reflective section 51 is the same as the display quality in the transmissive section. But also well known is an MVA semitransmissive liquid crystal display panel in which the structure for such cell gap adjustment is provided on the second substrate.
There will now be described, using FIGS. 6 and 7, an example of a related art MVA semitransmissive liquid crystal display panel 70 in which a top coat layer constituting a structure for such cell gap adjustment is provided on the second substrate. FIG. 6 is a plan view of a single pixel, seen through the second substrate, of a related art semitransmissive liquid crystal display panel in which the structure for the cell gap adjustment is provided on the second substrate, while FIG. 7 is a cross-sectional view along VII-VII in FIG. 6.
In this semitransmissive liquid crystal display panel 70, multiple scan lines 72 and signal lines 73 are each formed in a matrix, either directly or with an inorganic insulator 74 interposed, over a transparent glass substrate 71 possessing insulating properties, which is the first substrate. Each area enclosed by the scan lines 72 and signal lines 73 is equivalent to one pixel; a thin film transistor (TFT, not shown in the drawings) that serves as a switching element is formed in each pixel, and the surfaces of the TFT and other items in each pixel are covered by a protective insulator 83.
Further, in the reflective section 75 there is formed, so as to cover the scan lines 72, signal lines 73, inorganic insulator 74, protective insulator 83 and other items, a portion with a finely protruded and recessed surface, while in the transmissive section 76 there is deposited an interlayer 77 made of organic insulator with a flatly-formed surface. The concavoconvex portion of the reflective section 75 is omitted in FIGS. 6 and 7. A contact hole 80 is provided in the interlayer 77 in a position corresponding to the TFT's drain electrode D, and in the reflective section 75 of each pixel there is provided above the contact hole 80 and on the surface of the interlayer 77 a reflecting plate 78 made of aluminum metal for example. On the surface of the reflecting plate 78 and the surface of the interlayer 77 of the transmissive section 76 there is formed a transparent pixel electrode 79 made of indium tin oxide (ITO) or indium zinc oxide (IZO) for example.
Further, in the reflective section 75, an auxiliary capacity line 81 is disposed beneath the interlayer 77 in the position where the reflecting plate 78 is present; also, viewed from above, the reflecting plate 78 and pixel electrode 79 do not touch the adjacent pixel's reflecting plate and pixel electrode, and moreover are formed so as to slightly overlap to the same degree the scan lines 72 and signal lines 73, in order to prevent light leakage. In the transmissive section 76, the pixel electrode 79 does not touch the adjacent pixel's pixel electrode and reflecting plate, and moreover is formed so as to slightly overlap the scan lines 72 and signal lines 73.
Also, in this semitransmissive liquid crystal display panel 70, a slit 93 for controlling the orientation of the liquid crystal molecules is provided at the boundary region between the reflective section 75 and the transmissive section 76 of the pixel electrode 79, the pixel electrode 79 being divided into a pixel electrode 79a of the reflective section 75 and a pixel electrode 79b of the transmissive section 76, and the pixel electrode 79a of the reflective section 75 and the pixel electrode 79b of the transmissive section 76 being electrically connected via a narrow portion 94. Further, a perpendicular alignment layer (not shown in the drawings) is deposited over the surface of the pixel electrode 79 so as to cover all the pixels.
Also, over the display area of a transparent glass substrate 85 possessing insulating properties, which is the second substrate, there is provided a striped color filter layer 86, formed so as to correspond to each pixel, and being of any one of the colors red (R), green (G) or blue (B). Also, since a color filter layer 86 of the same thickness is used for the reflective section 75 and for the transmissive section 76, a topcoat layer 87 of a particular thickness is provided over the reflective section 75 portion of the color filter layer 86. This top coat layer 87 is provided over the whole of the reflective section 75 and has a thickness such that the thickness of the liquid crystal layer in the reflective section 75, or what is termed the cell gap d1, is one half the cell gap d2 of the transmissive section 76; that is, so that d1=(d2)/2.
Additionally, protrusions 91 and 92 for controlling the orientation of the liquid crystals are provided on, respectively, the portion of the color filter layer 86's surface that is located in the transmissive section 76 and the portion of the top coat layer 87's surface that is located in the reflective section 75, and a common electrode and a perpendicular alignment layer (neither of which is shown in the drawings) are stacked in that order on the surfaces of the color filter layer 86, top coat layer 87 and protrusions 91, 92.
The MVA semitransmissive liquid crystal display panel 70 is completed by positioning the first and second substrates to face each other, sticking the two substrates together by providing sealing around the peripheries thereof, and filling the space therebetween with liquid crystal 89 possessing negative dielectric anisotropy. Beneath the first substrate is disposed a public-domain backlight device having a light source, light guide plate, diffuser sheet and so forth, which is not shown in the drawings.
With this MVA semitransmissive liquid crystal display panel 70, in the state where no electric field is applied between the pixel electrode 79 and the opposing electrode, the liquid crystal molecules of the liquid crystal layer are oriented so that their long axes are perpendicular to the surfaces of the pixel electrode and the opposing electrode, and consequently light is not transmitted. On the other hand, when an electric field is applied between the pixel electrode and the opposing electrode, light is transmitted. This means that the device has the features that light leakage in the transmissive section will not much affect the display quality, and furthermore, thanks to the presence of the slit 93 in the pixel electrode 79 and the protrusions 91, 92, the liquid crystal molecules will incline toward protrusion 91 or 92, so that the viewing angle will be extremely wide.
In a semitransmissive liquid crystal display panel or reflective liquid crystal display device, the contact hole 80 formed in the reflective section is of a certain size and depth because it is necessary render reliable the electrical continuity between pixel electrode 79a and the TFT's drain electrode D, which serves as a switching element, and as shown in FIG. 7, the connector hole 80 is formed with inclined surfaces. Such inclining of the contact hole 80 imparts a physical force to the liquid crystal molecules 89, which causes the liquid crystal molecules 89 to incline as shown in FIG. 8. FIG. 8 is an enlarged view illustrating conceptually the liquid crystal molecules 89 in an inclining state at the contact hole 80 portion of FIG. 7.
A particular issue is that even when the liquid crystal molecules 89 are oriented by creating an electric field between pixel electrode 79a and the common electrode, the liquid crystal molecules 89, being strongly affected by the physical force of the contact hole 80, will not incline in the desired direction, and consequently exert an adverse effect on the display, so that the display quality deteriorates. Moreover, since the contact hole 80 is formed quite literally as a hole, the orientation of the liquid crystal molecules 89 is prone to be unstable from effects due to the presence of the contact hole 80, such as irregularity in the alignment layers—which are not shown in the drawings—and what is more, since the liquid crystal molecules 89 incline obliquely at the entrance portion of the contact hole 80 even when no electrical field is applied, blockage of light at this portion is incomplete, which may result in light leakage.
Further, in the vicinity of the protrusions 91, 92 formed in the second substrate, at the top surface portions of the protrusions 91, 92 the liquid crystal molecules 89 are oriented perpendicularly relative to the second substrate, but at the side portions of the protrusions 91, 92, are, under the influence of the incline angle of the side portions, oriented so as to be inclined obliquely relative to the second substrate. As a result, there exists the problem that when no electric field is applied, leakage of light from the vicinity of these protrusions occurs and the contrast deteriorates. Such a problem arising from the protrusions in an MVA liquid crystal display panel is disclosed in JP-2005-173105-A. With the invention disclosed in JP-2005-173105-A, there is set forth the provision of light-blocking films in positions corresponding to the protrusions, with the object of improving the contrast by preventing light leakage arising from disturbance of orientation due to the presence of the protrusions. However, no consideration is given to light leakage arising from the presence of the contact hole.